1. Technical Field
The present disclosure relates to a pneumatic tire having a designated tire inner side/outer side mounting orientation when mounted on a vehicle and particularly relates to a pneumatic tire that can enhance steering stability and high-speed durability during high-speed travelling without negatively affecting riding comfort.
2. Related Art
In recent years, there have been strict demands for reductions in the weight of pneumatic tires that are to be mounted on vehicles for which high-speed travelling is expected, such as sports cars and the like. However, for pneumatic tires that satisfy the demand for reduced weight, there is an additional demand of ensuring steering stability equivalent to or greater than that of conventional tires.
In order to meet these demands, pneumatic tires have been proposed including, for example, a carcass layer with a single-ply construction mounted between a pair of bead portions and a belt layer disposed on an outer circumferential side of the carcass layer corresponding to a tread portion, wherein the carcass layer is wrapped around bead cores disposed in each of the bead portions from a tire inner side to a tire outer side, a bead filler disposed on the bead cores is sandwiched between a main body portion and a wrapped portion of the carcass layer, and the wrapped portion of the carcass layer is extended to a lower region of the belt layer so as to overlap with an end of the belt layer.
Such pneumatic tires having a carcass layer with a single-ply construction that is extended to the lower region of the belt layer so that the wrapped portion overlaps with the end of the belt layer can exhibit superior steering stability due to the overlapping of the main body portion and the wrapped portion of the carcass layer in side wall portions while achieving a weight reduction effect due to making the carcass layer single-ply.
Additionally, a pneumatic tire having a designated tire inner side/outer side mounting orientation when mounted on a vehicle is proposed having at least two types of cap tread rubber layers, made from differing rubber compositions, disposed in the tread portion so as to be adjacent to each other in a tire width direction, wherein a tan δ at 60° C. of a rubber composition forming the cap tread rubber layer on a vehicle outer side is greater than a tan δ at 60° C. of the rubber composition forming the cap tread rubber layer on a vehicle inner side.
Steering stability can be enhanced by thus making the tan δ at 60° C. of the rubber composition forming the cap tread rubber layer on the vehicle outer side relatively greater. Additionally, while variations in steering stability performance due to heat generation easily occur when the tan δ throughout a entirety of the tread portion is increased, it is possible to suppress variations in steering stability performance caused by continued traveling while enhancing steering stability by making the tan δ at 60° C. of the rubber composition forming the cap tread rubber layer on the vehicle inner side relatively less.
However, with pneumatic tires to be mounted on vehicles for which high-speed travelling is expected, there is a demand for further enhancement of steering stability and high-speed durability during high-speed travelling, and that demand is difficult to meet. Additionally, it is also possible to enhance steering stability and high-speed durability during high-speed travelling by adding a reinforcing member to the tread portion and/or the side wall portions but, in these cases, there are demerits such as riding comfort being negatively affected, and the like.
An object of the present disclosure is to provide a pneumatic tire that can enhance steering stability and high-speed durability during high-speed travelling without negatively affecting riding comfort.